It is known to make reciprocating engine blocks from aluminum alloys such as the Al--Si alloys. Heretofore, eutectic and hypoeutectic aluminum-silicon alloy engine blocks have been made with iron cylinder liners for use with aluminum-silicon pistons. Iron liners, however, add weight and cost to the engine, and undesirably have a different thermal expansion than the aluminum block and piston. Alternatively, one engine manufacturer has made an engine block by positioning a porous preformed liner comprising alumina fibers and silicon carbide particles in a mold, and squeeze casting a hypoeutectic Al--Si alloy thereabout so as to infiltrate the preformed liner and form the cylinder wall. That engine was run with iron-plated pistons to avoid scuffing. Finally, blocks have been cast from hypereutectic aluminum-silicon alloy (e.g., 390 alloy), and the aluminum matrix etched back to expose hard silicon on the cylinder wall surface. These hypereutectic aluminum bore engines were run with aluminum pistons coated with iron, chromium, nickel, varnishes containing MoS.sub.2 or graphite, or ceramic oxide particles in an epoxy resin matrix (see Meise U.S. Pat. No. 4,395,442). See also, Rao et al U.S. Pat. No. 5,313,919, Rao et al U.S. Pat. No. 5,239,955, Presswood U.S. Pat. No. 4,831,977, Haldeman U.S. Pat. No. 3,890,950, and Fleming et al U.S. Pat. No. 2,817,562 for piston coated with lubricious films to reduce the sliding friction between the skirt and the cylinder wall. Some of those lubricious films comprise solid lubricious particles entrained in a heat resistant polymer matrix, and are known as "solid film lubricants" or "composite polymer coatings".
It is desirable to make engine blocks from eutectic or hypoeutectic Al--Si alloys, rather than hypereutectic alloys, because the eutectic and hypoeutectic alloys are cheaper and have good castability and machineability. It is likewise desirable to eliminate the iron liners and Al.sub.2 O.sub.3 --SiC preforms heretofore used with eutectic and hypoeutectic alloy blocks in order to reduce weight and cost, as well as improve heat transfer. However, running aluminum pistons against aluminum cylinder walls results in significant scuffing (i.e., adhesive wear between two parts sliding together in a lubricant-starved condition) of the cylinder walls and the piston skirts. Excellent scuffing resistance can be obtained between eutectic and hypocutectic blocks and aluminum pistons by coating the piston skirt with solid film lubricants. However, the wear resistance and durability of such coatings in this application is inadequate for a long-lived engine.